Don't know why people would downvote this. It's a pretty good idea of how to measure the value of a company. It's somewhat shy of the true metric which would be along the lines of 'how much better it made the world'. Market cap is appealing because it's trivial.

These definitions would also allow comparing non-standard corporations, like churches and states. It seems like this is a natural comparison - it's inevitable that big companies are ranked among comparable countries.